Aerodynamic fragmentation of water, ethanol and polyethylene glycol droplets investigated by high-speed in-line digital holography

Abstract

Digital holography is a remarkable interferometric technique for determining the size, shape, distribution, and spatial location of particles. Therefore, when combined with high-speed imaging technology, it represents a relevant technique for the study of the aerodynamic fragmentation phenomenon wherein the aerodynamic strengths counterbalance the cohesion forces of the drops causing thus their decomposition. We discuss in this paper the droplets fragmentation of water, ethanol and polyethylene glycol 300 solutions interacting with a shock wave and flow generated by an open-ended shock tube. In this context, a shock tube device was set up, and both the released flow as well as the shock wave generated were characterized by ultrafast imaging shadowgraphy and high speed pressure measurement. Millimeter diameter average drops are fragmented and imaged by high-speed digital in-line holography at a rate of 24800 fps, and then the image retrieved numerically. The Weber numbers are determined for each liquid and the observed fragmentation patterns are consistent with the description of the ‘chaotic regime’ reported in the literature by Pilch and Erdman (1987) [1].